n-digit number

An n-digit number is a positive number with exactly n Nine hundred distinct n -digit numbers are to be formed using only the three digits 2,5, and 7. The smallest value of n for which this is possible is (a) 6 (b) 7 (c) 8 (d) 9

Let a_(n) denote the number of all n-digit numbers formed by the digits 0,1 or both such that no consecutive digits in them are 0. Let b_(n) be the number of such n-digit integers ending with digit 1 and let c_(n) be the number of such n-digit integers ending with digit 0. Which of the following is correct ?

An n digit number is a positive number with exactly n digits. Nine hundred distinct n digit numbers are to be formed using only the three digits 2, 5 and 7. The smallest value of n for which is possible is

The numbers 2272 and 875 are divided by a 3-digit number N, giving the same remaindes. The sum of the digits of N is

N is a three-digit number. If exceeds the number formed by reversing the digits by 792. Its hundreds digit can be